1. Field of the Invention
The present invention relates to a writing power control method of a compact disc drive, and more specifically, the present invention discloses a writing power control method capable of determining an optimum writing power of a compact disc drive.
2. Description of the Prior Art
In general, document management and storage is an important concern of companies and individuals. In the past, most documents were printed or written on paper but when the quantity of these documents is large, the volume and weight of them becomes a problem. In parallel with the development of computer technology, digitalized data is widely used and stored by use of computer storage media. A wide variety of storage devices is available for allowing users to store digital data conveniently. A compact disc drive, which uses small, inexpensive and high capacity compact discs as storage media, is a popular and effective storage device.
Generally, before writing data onto a compact disc, the compact disk drive must perform an optimum power control (OPC) to determine an appropriate writing power of the compact disc. As to a preferred method of performing the OPC, details can be found in the Orange Book and are summarized as follows.
Please refer to FIG. 1. FIG. 1 is a diagram of a compact disc 10 when a compact disc drive performs the OPC on the compact disc 10 according to the prior art. When the compact disc drive performs the OPC, a pick-up head 11 of the compact disc drive first retrieves an indicative optimum writing power P from a lead-in area 12 on the compact disc 10. The indicative optimum writing power P is an appropriate writing power of the compact disc 10 that a compact disc manufacturer suggests. Then, the pick-up head 11 uses fifteen writing powers, which comprises seven writing powers, P1 to P7 , less than the indicative optimum writing power P, the indicative optimum writing power P itself, and seven writing powers, P8 to P14, greater than the indicative optimum writing power P, to perform a writing procedure in fifteen successive blocks 18 of the test area 16 of the compact disc 10.
After performing the writing procedure, the pick-up head 11 will retrieve a result written to the blocks 18 as a read-back signal. The read-back signal is an AC coupled HF signal. The Orange Book has defined a symmetrical parameter β determined from the read-back signal. When the symmetrical parameter β of the read-back signal corresponds to a predetermined requirement, the corresponding writing power can serve as the actual optimum writing power of the compact disc 10. After retrieving the test results of the fifteen writing powers, the pick-up head 11 obtains the symmetrical parameter β values (β values) of the fifteen read-back signals corresponding to the fifteen writing powers. Then, the compact disc drive compares the β values of the fifteen read-back signals with a target β value stored in the lead-in area 12 of the compact disc 10. If the smallest difference between the corresponding β value of one of the fifteen writing powers and the target β value is less than a predetermined value, the writing power corresponding to the above β value is the optimum writing power. If the differences between the corresponding β values of the fifteen writing powers and the target β value are all greater than a predetermined value, the fifteen writing powers are all unsuitable to function as actual writing powers. Consequently, additional groups of fifteen writing powers need to be selected to perform the optimum writing power control until an optimum writing power is obtained.
The aforementioned writing power control has two main shortcomings. First, the method uses a trial and error approach without the benefits of recursion. If the initial fifteen writing powers selected are inadequate, additional time must be spent in successive trials. Second, the aforementioned writing power control utilizes different writing powers during a short time interval. It is easy for the pick-up head 11 to accidentally move to the next block to produce an incorrect etching depth during the writing test because of the unstable writing power. As a result, erroneous β values may be obtained, which further influences the accuracy of the determined optimum writing power, and ultimately writing quality.